Switch and plug box



1948. w. J. BAUROTH SWITCH AND PLUG BOX Filed May 1, 1943 3 Sheets-Sheetl w ON y k l/vvElvroei WALTER J. BAUEOTH, BY C W.

, May 1948- w. J. BAUROTH SWITCH AND PLUG BOX Filed May 1, 194:5

3 Sheets-Sheet 2 Rm Mr? K g E y 1, 1948. w. J. BAUROTH SWITCH AND PLUGBOX 5 Sheets-Sheet 3 Filed May 1, 1943 WALTER J. BAuEoTH,

BY MM QR S o mw Ynfirw T 8 N $1 .1 3 w 9. I s \\\\\A\k l m m I n m P. nw

I l I I I I I I I I I III IIIIIIII VIII-Mm In Q 3 X Q Patented May 11,1948 UNITED STATES PATENT OFFICE SWITCH AND PLUG BOX Application May 1,1943, Serial No. 485,291

1'7 Claims. 1

This invention relates to a switch or circuit breaker and plug box whichis designed particularly for use in a gaseous mine such as a coal minethough it may have many other uses.

An object of the invention, therefore, is to provide an improved switchand plug box of the so-called permissible or flame or explosion-prooftype.

A more specific object of the invention is to provide a device of theabove-mentioned type in which the electrical disconnectible plug is in apermissible or flame or explosion-proof compartment of the box which isseparated from another permissible or flame-proof compartment containinga control switch.

A further object of the invention is to provide apparatus ofthe'above-mentioned type in which a control switch is in one permanentflameproof compartment and is connected to a disconnectible plug in acompartment which may be selectively open or closed and when closed isof the flame-proof type and in which there is mechanism operable fromthe plug compartment to control the switch in the switch compartment.

Another object of the invention is to provide apparatus of theabove-mentioned type in which a plug is locked in position in itsflame-proof compartment and when so locked automatically closes theswitch in the switch compartment, said switch being automatically openwhen the looking mechanism of the plug is adjusted to permit removal ofsaid plug.

Another object of the invention is to provide an improved type ofelectrical plug having locking mechanism associated therewith as well asswitch operating mechanism associated therewith.

A further object of the invention is to provide as an article ofmanufacture a plug sleeve having a lug including locking means andpreferably an operating cam or key formed as an integral part thereof.

Other objects of the invention will appear hereinafter, the novelfeatures and combinations being set forth in the appended claims.

In the accompanying drawings,

Fig. 1 is a sectional elevational view of the device of my invention,certain parts not being shown entirely in section in the interest ofclearness;

Fig. 2 is a sectional view taken on the line 22 of Fig. 1, looking inthe direction of the arrows;

Fig. 3 is a sectional view taken on the line 33 of Fig. 1, looking inthe direction of the arrows;

Fig. 4 is an enlarged plan view of a portion of the box and plug withthe operating sleeve of the plug shown in developed relation;

Fig. 5 is a plan view of the device of my invention with parts brokenaway and in section and with certain parts omitted in the interest ofclearness;

Fig. 6 is a front elevational view of the device;

Fig. 7 is a view of a portion of the plug compartment with the operatingsleeve moved to the switch closing and plug locking position;

Fig. 8 is a view similar to Fig. 5 of a modified form of my invention inwhich two switches are housed within a flame-proof compartment and arecontrolled by common operating mechanism;

Fig. 9 is a sectional view taken on the line 99 of Fig. 8, looking inthe direction of the arrows, showing particularly the operatingmechanism for one of the switches;

Fig. 10 is a sectional view taken on the line |n |n of Fig. 8, showingthe operating mechanism for the other switch; and

Fig. 11 is a wiring diagram showing the connections to the miningmachine motor and the auxiliary motor.

In gaseous mines such as gaseous coal mines it is necessary in order tomeet the requirements of the Bureau of Mines to provide what is known aspermissible or explosion or flame-proof equipment and to this end it isnecessary to prevent the exposing of any electrical conductors, plugs orthe like, in which it is possible to have the exposed conductors orplugs energized even though current may not be flowing in them. In otherwords, a voltage must not be present on any exposed electricalconductors or plugs.

In the apparatus which I have provided, a disconnectible plug isprovided and mechanism which forms a permanent part of the complete plugis provided to control a switch which disconnects the plug from thesource of voltage before the plug can be exposed, the plug itself beingcontained in an explosion, or flame-proof compartment when it is in anelectrical conducting condition.

Referring to the drawings it will be seen that I have provided apermissible, explosion or flameproof box, housing, or enclosure Illwhich in cludes a relatively large switch compartment or enclosure IIand an integral extension forming a plug compartment, housing orenclosure [2. The bottom, side and end walls of the explosion orflame-proof switch compartment l I are integrally formed of suchmaterial as cast iron and the top is formed by a removable top plate l3,removably attached by a plurality of machine screws M. The rear wall ofsaid compartment H is provided with a pair of stufiing boxes eachadapted to receive a single conductor cable and provide a flame-proofconnection therewith.

In some arrangements which I have provided, a plurality of boxes 10 aremounted upon a com mon base and are electricaly interconnected and tothis end the rear of the compartment H is also preferably provided withopenings [6 on opposite sides thereof which, when a single box iseniployed, is either filled by a removable plug or the Opening is notactually formed but is cast solidly close together with the sidewalls OIthe box 13. The two cables received by the stuffing boxes [5 lead to asource of potential and consequently they are always energized or hotand these cables are connected within the compartment H to the receivingterminals of a combination switch and overload circuit breaker H.

The plug compartment l2 includes an integrally formed neck 18 whichextends horizontally and forwardly from the front wall of thecompartment H and this neck receives a sleeve lfi having a peripheralouter rim 20, the sleeve 19 being connected to the neck [8 by fourspaced machine screws 2| (see Fig. 6). The inner end of the sleeve I3includes ah integral wall 22 which wall acts as a partition to dividethe plug compartment 52 into two parts and acts to support two separableparts of an electrical receptacle or socket 23 which is made of ir llilatiilg material arid which is connected to the paitition 22 by threebolts 22 (see Fig. 2). Said bolts 24 extend through three openings whichcan be seen at 25, particularly in Fig. 6 of the drawings, said openings25'being formed in integral wings of the partition 22 that extend into acentral steam-g 26 formed in the partition 22, as illustrated in dottedlines in Figs. 2 and 6 of the drawings. Said central opening 26 providesfor the eiite'ns'icn therethrcugh of bayonet type receiving coritactswhich are provided in the receptacle 23, this type of electricalreceptacle being well kncwn in the electrical art.

It may be mentioned that the plug or receptacle 23 includes an innerpcrtion 21 which has three terminals 28 which are connected to threeelectrical conductors renting part of a short cable 29 which extendsthrough a smiling box 30 carried by a pair or arms 3|, said s'tuifiingbox 30 having a fiarne-procf fitting betwe'e'h the outer cylindricalsurface thereof and a cylindrical opening in the front w all of theswitch compartment H, thus providing a permissible or flame-proofpasageway for the conductors of cable 29. In said compartment ll two ofthe conductcrs of cable 29 are connected to the output terminals of theswitch I! and the third conductor thereof is the ground conductor whichis grounded to the box l0 within 's aid compartment II, as is clearlyillustrated in Fig. i or the drawings, by being connected to a p r djectiloh formed integrally with said box l0 and within the compartm'eht H.

The receptacle 23 also includes an outer portion 32 which is outside orto the left or the partition 22, the two "portions 21 and 32 of saidreceptacle 23 b ing held together and mounted on the partition 22 by thebolts 24, as above described. Said 'o'uter receptacle portion 32 carriesthree bayonet receiving contacts to receive the three bayonet prongs ora removable luses hereinafter described more completely, said plug andreeeptauejstrucmre being of a type Well known in the electrical art.

Mounted upon the end of a' three conductor am ss electrical cable 33,which electrical cable may be the source of power for any desired pieceof apparatus, I provide what I shall designate as a complete plug 34. Itmay be stated that the electrical apparatus to which energy is suppliedby the cable 33 may be of any type. By way of illustration it may bestated that the apparatus of my invention has been employed in coalmining apparatu's' in which the cable 33 energizes electrical drills fordrilling the mine face in a coal mine and electrical water wagons whichprovide water to spray the mine face while a cutting machine is cuttinga kerf. These are only two illustrations or which many might be given ofthe type of apparatus in' which my device may be employed.

Referring particularly to the structure of the complete plug 34,attention is directed particularly to Figs. 1, 5 and '7 of the drawings.Said complete plug 34 includes a plug holder or main body 35 whichincludes a handle 36 by which the plug may be connected or disconnectedand also includes a cylindrical housing portion 31. Within the housingportion 31 is mounted an electrical insulated plug 33 provided withthree bayonet type blades adapted to be projected into theaforementioned electrical contacts carried by the receptacle 23. Theelectrical plug 38 is attached by three spaced screws 39 to integrallyformed ears provided within the hollow interior of the plug holder 35.Rotatably' mounted on the outer cylindrical surface of the housingportion 31 is a generally cylindrical sleeve 40 which is provided with aplurality of radially extending lugs 4| (see Fig. 6) which are adaptedto be gripped by an operator to rotate said sleeve 43 for the purpose oflocking the complete plug 34 in place and simultaneously operating theswitch I! to close its circuit, as hereinafter described morecompletely.

The sleeve 40" is also provided with a stop member 42 adapted tocooperate with a stationary stopmernber 43 carried by the rim 2'!) ofsleeve 19 to limit rotary motion of said sleeve 40 in acounter-clockwise direction. The sleeve 40 is preferably made as a brasscasting and, of course, the interior surface thereof is cylindrical andof appreciable longitudinal length so as to have contact over a largebearing area with the outer cylindrical surface of the housing portionof plug holder 35. Also the outer surface of the sleeve 40 iscylindrical and has an appreciable bearing area with the innercylindrical surface of the sleeve l 9.

These two relatively large bearing surfaces between the sleeve 4? andthe housing portion 31 in one instance and the sleeve IS in the otherinstance are for the purpose of insuring a permissible, explosion orflame-proof construction for the plug compartment I2. In other words,should an explosion take place within said compartment I2, due to itbecoming filled with explosive gas in a gaseous mine, which gas wasignited by an electric spark, the explosion in the compartment 12 wouldnot be capable of discharging a flame outside said compartment. This isbecause the hot expanded gases resulting from the explosion would haveto travel over such elongated paths along the surface'spn both theoutside and insideof the sleeve '48 as to 0001 said gases sufilcientlyto prevent the appearance of a flame outside said compartment l2. Thesleeve "0 is mounted 'for rotary movement with respect to the plugholder 35 as previously described but after being once assembled itbecomes a permanent part of the complete plug 34 and is held againstlongitudinal movement with respect to said plug holder 35 by virtue ofthe fact that the inner end of the cylindrical housing 3'! is. providedwith a peripheral ledge 44 adjacent which the inner end of thecylindrical housing 31 abuts. The outer end of the sleeve 40 is heldagainst longitudinal movement with respect to the plug holder 35 by awire ring 45 which fits into a groove in said plug holder 35 and theends of which are perfectly welded together after it is inserted in saidgroove.

It is an important feature of my invention that after the complete plug34 is inserted in place to effect an electrical connection and with theparts in position as illustrated in Fig. 1 of the drawings it ispossible by rotating the sleeve 48, by grasping the lugs 4 I, to lockthe complete plug 34 in place, thus preventing its removal andsimultaneously closing the switch I! by moving it to the on position. Tothis end the sleeve 40 is provided with a lug or actuator in the form ofan integral extension or key 46 which is formed as a segment of acylinder and which is provided with an arcuate slot or groove 41 (seeparticularly Fig. 4) which groove upon rotation of the sleeve 40 in aclockwise direction from the position illustrated in Fig. 1 to theposition illustrated in Fig. 7 receives a portion of the partition 22and as a consequence will prevent removal of the complete plug 34 andthus will prevent breaking of the electric circuit by the electricalplug 38 and receptacle 23.

At the same time that the complete plug 34 is thus locked in position itsimultaneously is effective to close the switch I! (which switch I1otherwise cannot be closed) by moving the switch operating mechanismhereinafter described. To this end there is provided within the switchcompartment II a longitudinally extending operating rod 48 slidablymounted in a bore 49 formed in a boss 50 at the rear end of the switchcompartment l I and sliding through a bore in a boss 5| (see Fig. 4) inthe front wall of said compartment ll.

The rod 48 of the switch operating mechanism is provided with a yoke 52(see Fig.3) which has sliding contact with the top plate [3 and which isremovably attached to the rod 48 by a screw 53. The yoke 52 acts as oneabutment for a coil spring 54 which is coiled about the rear end of therod 48 with the opposite end abutting the boss 50, As a'consequence ofthis structure the rod 48 is held against rotation and is mounted forlongitudinally sliding movement and is resiliently urged or held in oneposition, that is, to the left as viewed in Figs. 1 and 5 of thedrawings.

Intermediate its ends the rod, 48 is provided with a transverse groove55 which receives an operating member 56 of the switch l1, said groove55 being provided on opposite sides of said member 56 with removableleather blocks 51 to provide cushion means for the operating member 56.

With the members in the positions illustrated in Fig. 1 of the drawings,the switch I1 is in the off or open circuit position and. to move it tothe on or closed circuit position the rod 48 is shifted to the rightcarrying with it the operating member 56.

It may be stated that if the overload relay of the combined switch andrelay l1 opens in response to excessive current, this will take placeonly when the switch I! is closed and to reset the overload relay theoperating member must be moved to the 01f position and then to theonpositlon which can be effected, of course, by operating the rod 48.

The left-hand end of the rod 48 extends into th plug compartment l2 andas particularly illustrated in Fig. 4 of the drawings it is to be notedthat the extreme left-hand end of said rod 48 is positioned adjacent andbehind a portion of the partition 22. As a consequence, it ispractically impossible for anybody to manipulate the rod 48 except byinserting the complete plug 34 and rotating the sleeve 40 to effect itsoperation in a manner now to be described.

It may be pointed out that the lug, extension or key 46 of the sleeve 40extends through a very narrow arcuate elongated slot 58 (see Fig. 2)which is formed in the partition 22 and when the parts are assembled asillustrated in Fig. 1 of the drawings this elongated slot 58 is the onlyeffective opening in the partition 22 since all other openings have beenclosed by the receptacle 23.

It is to be noted that due to the small width of the slot 58 it would beextremely diflicult for any person to extend a tool into it and get aworking contact with the rod 48 to move it, particularly in View of thefact that the left-hand end of the rod 48 is behind a wall of thepartition 22. This difficu-lty is further increased by the fact that theend of the rod 48 is provided with an anti-friction roller 58 and if atool such as a screw driver would project through the slot 58 it couldnot easily be caught on the rod 48 because the roller 58 would tend tocause it to roll off. The roller 59 provides an anti-friction bearingbetween the operating rod 48 and a cam surface 60 which is formed on theextension or key 46. Thus unauthorized closing of switch I! is preventedwhen plug 34 is removed. This precludes energization of the contacts incompartment l2 except when it is in a flame-proof condition.

It is obvious that when the sleeve 40 is rotated in a clockwisedirection from the position illustrated in Fig. 1, the cam surface 68(see Fig. 4) will contact with the roller 59 forcing the rod 48 to theright, as viewed in Figs. 1, 4 and 5, and continued rotation of saidsleeve 48 and extension 46 will move the rod 48 sufficiently to theright against the action of the spring 54 to operate the member 56 tomove the switch I! to the circuit closing or on position. This onposition of the rod 48 and roller 59 and the cam surface 68 isillustrated in Fig. 7 of thedrawings and the position of the roller 59is indicated in the on position in dotted lines in Fig. 4 of thedrawings, both with respect to its position on the rod 48 and withrespect to its position relative to extension or key 46. Thus with thesleeve 40 rotated in a clockwise direction with the parts all assembledthe switch I! will be on and the completeplug 34 will be locked so as toprovide the complete flame-proof character of the plug compartment l 2.

It may be noted that the cam surface 60 provides a hump on the extensionor key 48 which will frictionally hold the parts in the on or circuitclosing position as illustrated particularly in Fig. 7 of the drawings.

The operation of the device is believed clear from the above descriptionbut to review it briefly it will be assumed that if an operator desiresto connect an electrical drill which is provided with the electricalcable 33 and a complete plug 34 the complete plug 34 will be inserted byinsorting the sleeve 48 into the sleeve l9. To insure the properposition of the parts, the top of 7 the handle is preferably providedwitha; label, marked Top as illustrated in Fig. f oi the drawings;

It is, of'course, necessary thatthebayonet contacts oi the plug 38 bereceived properly bythe' receptacle 32 and to insure this alignment theplug has a fixed relation to the cylinder housing portion 31. of theplug holder v which isde't'ermined when the parts are rigidly assembledand this is determined by a small pin 6 I (see Rig-'79 whi'chprojectsinto a notclr 62 the pin at being carried by the cylinder housingportion fl and the notch 62 being formed in the electrical plug 38'; Theplug holder 35 can have only one position with respect to the sleeve I 9and this i'sefiected by virtueof a pin- 63- (see Fig. 2 which is carriedby the partition 22 and= which-projects into a slotor groove 64: formedon the inner. end of the plug holder 35. These two cooperatingparts' 63and 64, of course, prevent-rotation or the plug holder 35 when thesleeve 4!] is rotated t'o lock the complete plug 34 and to operate theswitch: l-l.

Assuming, therefore, thatthe parts have: been inserted as abovedescribed, the electric contact will be made between the electrical plug38 and receptacle 23 to" complete the electric circuit to the switch I1from the cable 33. The plug compartment I? will nowbe completelyclo'se'dprovldi'ng a flame-proof or permissible compartment. The sleeve- 40 willthen be rotated byan operator grasping the lugs 4 1, which are in thenature of anoperating handle for rotating said sleeve 40' in aclockwisedirection. When this rotation is completed the complete plug 34 will belocked' in position by virtue of the slot receiving a portion of thepartition 221 This, of course, will prevent removal of the complete plug34 until sleeve 49- is rotated to a reverse position.

The condition of the parts with said complete piugil'locked isillustrated-in Fig. 'Tcf thed'ra-vw ings. This rotary motion in additionto locking thecomplete plug 34 will also close the switch I1- by'movin'gthe operating rod 48 against the actionof the spring 54 or; inotherword's; move it to-lts=on-'position. This is effected bythe-camsurface 61F of the extension or key 46 pressing againstthe-anti-friction roller is and consequently-forcing the operating rodMl-rearwardly, which movement operates the member 56 to close the switchH. The form of the cam'suriace' Bil with theflnal on position, will tendto'ho'l'd the'parts in the on or locked position, thesaid spring pressedroller 59 operating as a spring detent.

Afterthe drill has been used to-the extent desired; in case'it'isdesired to-disconnect the-cable so: as totake the drill to anotherpart" of the mine,- the handleprovided by thelugs 41'" will be rotatedin a counter-clockwise direction and-under the action of the spring 5the-rod 48 will move to the left, or forwardly'to openthe switch ll, ormove it to its oil position; and thecompl'ete-plug 34 will'b'e free sothat it" can bepulled outby longitudinal pull on the h'andle'35:

It is to be particularly noted that the switch compartment II is aflame-proof compartment under all conditions. The plug compartment I2 ismade flame-proof whenever the complete plug 33' is inserted and it isimpossible to energize any of-the'electrical connectors in the plugcompartment [2 until the complete plug 34- has been locked in" positionbecause the locking of' said complete-plugin position is a necessaryincident to the operation of the control switch Hi It is also: evidentthat have. made it extremely dimcult, ii: not impossible, for any one tooperate the switch- IT to its- "on or closed position except byinserting the complete plug 34 and adjusting it to its locked-position.As a consequence, it is practically impossibleto provide a voltage inthe plug compartment I 2, by any manipulation of switch I-"I, exceptwhen the complete plug 35 is locked i'n-pla'ce and said plug compartmentor housing I 2 is closed and flame-proof in character. In other words,when the plug 34is'removed, the receptacle 23' is dead.

In" Figsi- 8', 9' and 10 of the drawings I have shown a modifiedarrangement in which the structure is the'sa-me a-s that previouslydescribed unlessa contrary fact is indicated. In this'modlfled structureI have provided a toggle switch 65 which is placed inthe switchcompartment ll alongside the switch IT. The toggle switch 65 controls amotor which drives the cutter chain 01" a mining machine and this switch65 and switch I'l' are so interlocked that the former is in the oilposition while the latter is in the on position and vice versa. This isan important safety feature and precludes operation of an auxiliarymotor'such as a hand-operated electric drill except when the cuttingmechanism of the mining'machine'is shut off. To'provide this interlock,an operating arm 66 is carried by the 1 rod 68. and this arm 66preferably is provided with spaced contact bearing'lugs' 61 which havesliding frictional contact with the cover plate I 3". The ar'nrGGTi'sshown L-shaped and the outer end thereof is' provided with a U-shapedyoke 68 (see'Fi'g. 10') which straddles the operatingmember 69 or the.switch 65'. As illustrated in' Figs. 8,, 9 andlOof'the drawingstheswitch I1 is open or is in the ofl'position. When the rod 48 ismoved'lto the right, as viewed in Fig. 8, by the operation. of the" camsurface 60, as previously describedi'n' connection with Figs; 1 to '7;inclusive; the rod 48 will be moved to the right and switch l1 will beclosed while switch will be open.

The electrical circuit in which two switches I1 and as well as thecomplete plug 34" and assoelated. cable 33 are an. important part, isillustratedin'FigI 11 of the drawings; As here illustrated, the motor 10is,.for example, the motor which" drives the cutter chain of a miningmachine and purely" by' way or illustration it may be si'miiar'to themotor illustrated in detail in Fig: 37of the patent to R; K. Jeiirey'etall, 2,263,- 779; dat'edi November 25, 1941'. This electric motor isenergizedfroma pair or mainline conductors H and is controlled by amagnetic contactor or switch 12, that is, the switch or contactor' l2controls thei. energization of motor 10 from conducto'rs ll Thecontactor 12' is under the control of the toggle switch 65: and astarti'n'g" switch T4 over an obvious circuit so that whenever thetoggle'switch 65 is closed or in its onp'ositlon' the c'ontactor'llmaybe energized by closing". the switch 14 to drive the motor 10andwlientoggle switch 65 is open or in its oii" position; contact'or' 12cannot" be energized to start thefmotor' 101 Branch conductors leadir'ommai'n' conductors ll directly to switch I] whichcontrolstheconductorsofshort cable 29 andofr cable 33through the pl'ugi38an'd'receptacle 23. Cable 33' leads to an auxiliary motor" 13 which may be"the. motor of": any auxiliary apparatus; one illustration of whichmaybethe motor of a hand drill'such as illustratedinPatent'No. 2,159,087 toR. K. Jei- 9 trey, dated May 23, 1939, This hand drill is understood tobe only one illustration of various types of equipment which may beattached to cable 33.

In addition to the features above described in connection with thedevices of Figs. 1 to 7, it is evident that the devices of Figs. 8 to 11provide a safety feature, in that the auxiliary device such as the handdrill, can only be operated when the circuit to the cutting motor of themining machine is open. As a consequence, an operator working at theface of a mine room is protected against the extreme hazard which mightotherwise be occasioned by the operation of the cuting mechanism of themining machine.- The features of invention herein described inconnection with Figs. 8 through 11 are claimed in my copendingapplication, Serial No. 13,648, filed March 8, 1948, for improvements inElectrical circuit including a switch and plug mechanism.

Obviously those skilled in the art may make various changes in thedetails and arrangement of parts without departing from the spirit andscope of my invention as defined by the claims hereto appended, and Itherefore wish not to be restricted to the precise construction hereindisclosed.

Having thus described and shown an embodiment of my invention, what Idesire to secure by Letters Patent of the United States is:

1. A device of the class described including an explosion-proofenclosure, a circuit controlling switch in said enclosure, adisconnectible electrical cable plug and receptacle carried outside saidenclosure and connected to said switch, mechanism for operating saidswitch including operating means located entirely within said enclosure,means preventing operation of said operating means by an operator, andactuating means carried by said plug for .actuating said operating meanswhen said plug is inserted in its receptacle.

2. A device of the class described including an enclosure, a circuitcontrolling switch in said enclosure, a disconnectible electrical cableplug and receptacle carried outside said enclosure and connected to saidswitch, mechanism for operating said switch including operating meanslocated entirely within said enclosure, means preventing operation ofsaid operating means by an operator, and actuating means carried by saidplug for actuating said operating means when said plug is inserted inits receptacle.

3. In electrical circuit controlling apparatus, an explosion proofswitch box, a connected explosion-proof plug and receptacle housing, a 7

switch in said switch box, a plug and receptacle in said connectedhousing connected with said switch, mechanism providing for closing saidswitch, means preventing operation of said switch closing'mechanism byan operator when said plug is removed from said receptacle, and meansassociated with said plug providing for operation of said switch closingmechanism when said plug is in the receptacle.

4. In electrical circuit controlling apparatus, an explosion-proofswitch box, a connected explosion-proof plug and receptacle housing, aswitch in said switch box, a plug and receptacle in said connectedhousing connected with said switch, mechanism providing for closing saidswitch, means preventing operation of said switch closing mechanism byan operator when said plug is removed from said receptacle, andmechanism for locking said plug in said receptacle and actuating saidswitch closing mechanism, said switch closing mechanism being operableonly by said locking mechanism and requiring said switch to be openedbefore said plug can be removed.

5. In electrical circuit controlling apparatus, an explosion-proofswitch box, a connected explosion-proof plug and receptacle housing, aswitch in said switch box, a plug and receptacle in said connectedhousing connected with said switch, mechanism providing for closing saidswitch, means preventing operation of said switch closing mechanism byan operator when said plug is removed from said receptacle, andmechanism for locking said plug in said receptacle and actuating saidswitch closing mechanism, said switch closing mechanism being operableonly by said lockin mechanism.

6. A combination switch and plug box including an explosion-proof switchcompartment, a control switch in said compartment, an explosion-proofplug receptacle compartment, a plug receptacle in said receptaclecompartment, an operating lever for said switch extending from saidswitch compartment into said plug receptacle compartment and operable inopposite di rections to operate said switch to off and on positions,respectively, conductors connecting said switch and plug receptacle, anelectrical contacting plug having conducting means constructed forinsertion into electrical contact with said receptacle and removaltherefrom, means for simultaneously locking said plug in said receptaclewhen they are connected and operating said lever to move said switch toits on position, and means preventing operation of said lever except bysaid last-named means.

-7. In a switch and plug box, an explosion-proof compartment, a switchin said compartment, an operating lever for said switch, a, plugreceptacle connected with said switch, a removable plug insertable insaid receptacle, means preventing access to said operating lever by anoperator, and mechanism carried by said plug for operating said lever toclose said switch and lock said plug in said receptacle when said plugis in said receptacle.

8. In a switch and plug box, an explosion-proof compartment, a switch insaid compartment, an operating lever for said switch, a plug receptacleconnected with said switch, a removable plug insertable in saidreceptacle, means preventin access to said operating lever by anoperator, and mechanism carried by said plug for operating said lever toclose said switch when said plug is in said receptacle.

9. In a switch and plug box, an explosion-proof compartment, a switch insaid compartment, an operating lever for said switch, a plug receptacleconnected with said switch, a removable plug insertable in saidreceptacle, means preventing access to said operating lever by anoperator, and mechanism carried by said plug for operating said lever toclose said switch and lock said plug in said receptacle when said plugis in said receptacle, said mechanism including a rotary sleeve having alever operating key and having a locking groove fitting over andinterlocking with a member on said box when said sleeve is rotated tolocking position.

10. In a switch and plug box, an explosionproof compartment, a switch insaid compartment, an operating lever for said switch, a plug receptacleconnected with said switch, a removable plug insertable in saidreceptacle, means preventing access to said operating lever by an

